The overall objectives involve the application of multinuclear NMR techniques to study the molecular details of complex biochemical systems. The strategy is to focus on a particular aspect of the complex system for example, the active site of an enzyme, reactive intermediates in the enzyme mechanism. This is accomplished by the observation of less abundant nuclei or by specific labeling procedures (biosynthetic or chemical) with enriched nuclei. Understanding the chemistry of metal ions in metalloenzymes is an essential prerequisite to an understanding of the direct or indirect role of the catalytically essential metal ion in the overall enzymatic mechanism. Substitution of 113Cd2 ion for the native Zn2 ion(s) in these enzymes has been shown to provide a sensitive NMR probe and biologically relevant analogue (toxicological role) with which to study the structure and dynamics of the active site metal ion Carboxypeptidase A, superoxide dismutase, aspartate transcarbamylase, metallothionein, carbonic anhydrases and alkaline phosphatase are among the metalloenzymes which will be studied. The later two systems serve to illustrate here the specific information which is sought; the exact molecular details responsible for the 10 fold difference in the catalytic activity of the two isozymes of carbonic anhydrase from human red cells, characterization of the nature of the allosteric interactions responsible for the apparent negative cooperativity exhibited by alkaline phosphatase, detailed explanation of the role of the catalytic and structural metal ions in this enzyme in particular, the nature of the relationship between metal ion stoichiometry and phosphate stoichiometry, catalytic activity, and structural stability. The fusion of cells or intracellular vesicles has been shown to depend on Ca2 ion levels. In model membranes 113Cd2 ion reproduces Ca2 ion fusion phenomenon and thus provides a probe with which to study the mechanism of fusion. Structural details of the DNA binding groove and the nature of the Gene 5 Protein-DNA complex will be determined. Details of this interaction will provide a model for understanding the structural characteristic and binding determinants of other DNA binding proteins.